MCT will be performed according to the ATS guidelines for the Methacholine Challenge Test. Tests will be performed in a designated room at the Pediatric Pulmonary Unit, Meyer Children’s Hospital, Haifa, Israel. A parent and the investigating team will be present throughout the test. Tests will be performed with triple doses of fresh Methacholine solutions (0.057 to13.395 mg/ml) dissolved in saline. Solutions will be driven by a KoKo-PDS dosimeter (Ferraris Respiratory, Louisville, CO) via mouthpiece while the child was sitting upright with a nose-clip and breathing at least 10 deep breaths. Five-minute intervals will be taken between concentrations until the maximal concentration or the end point will be reached (see below). Oxygen saturation and heart-rate will be monitored continuously by pulse-oximetry (Ohmeda Biox 3700 Pulse Oximeter, USA). Auscultation for 20-seconds over the trachea and two zones of both lungs (upper front and lower back) will be performed according to recommendation. The following indices will be considered as EOT: appearance of audible wheeze, a fall of 5% in O2-saturation, or an increase of 50% in respiratory rate and/or heart rate. Nebulized Albuterol (2.5mg) was administrated after lung function measurements.